Many forms of thermal management exist today all of which depend upon the principles of conduction, convection, or radiation to move heat. Good thermal conductivity is required to permit heat transfer away from high density electronic components and devices such as integrated circuits. High thermal conductivity materials are conventionally used in heat transfer devices to dissipate heat from semiconductor circuits and systems. Heat transfer devices with high thermal conductivity materials may also be utilized in aerospace and military applications. Elemental metals are not satisfactory for the semiconductor circuit systems in use today. This has led to the use of high conductivity heat transfer devices formed from composites or laminations of different materials fabricated into various structural assemblies which will possess the desired high thermal conductivity, strength, and other needed properties.
A heat sink is a thermal dissipation device comprised of a mass of material that is internally coupled to a heat source to conduct thermal energy away from the heat source. Heat sinks are typically designed to transport the heat from the heat spreader on the integrated circuit to ambient air. The heat sink may be in the form of fins or integrated heat spreader. The heat sink conducts the thermal energy away from a high-temperature region (e.g., the processor) to a low-temperature region (e.g., the heat sink). Thermal energy is then dissipated by convection and radiation from the surface of the heat sink into the atmosphere surrounding the heat sink. Heat sinks are typically designed to increase the heat transfer efficiency by primarily increasing the surface area that is in direct contact with the air or liquid. This allows more heat to be dissipated and thereby lowers the device operating temperature.
Heat sinks used for cooling electronic components typically include a thermally conductive base plate that interfaces directly with the device to be cooled and a set of plate or pin fins extending from the base plate. The fins increase the surface area that is in direct contact with the air or liquid, and thereby increase the heat transfer efficiency between the heat source and ambient.
In conventional heat sinks, the base and/or the fins are typically either copper or aluminum. Copper and aluminum have relatively high coefficients of thermal expansion (CTE). Electronic components, including semi-conductor materials in those components, are typically formed from a material having a low CTE (4˜7×10−6/° C.). While copper and aluminum exhibit good thermal conductivities, a large mismatch in terms of differences in the CTE of the heat sink material and the electronic component(s) may introduce excess stress to the mounted electronic components (e.g., semi-conductor chips), which may lead to failure or unreliable operation. Low CTE materials such as aluminum silicon carbide (AlSiC), molybdenum-copper alloys, tungsten-copper alloys, or copper-molybdenum laminates have been used for heat sinks. These materials have low thermal conductivities, and the use of these materials in heat sinks generally sacrifices thermal conductivity for better CTE matching with the electronic components.